The term heterochromatin refers to a highly condensed form of chromatin. It accounts for approximately 30 percent of the genome in higher eukaryotes. Heterochromatin has been implicated in processes as diverse as chromosome pairing and segregation, rearrangements, speciation and recombination. The long term goal of this project is to understand the structure and function of heterochromatin. The investigators have identified a heterochromatin-specific nonhistone chromosomal protein designated as HP1. The gene encoding HP1 has been isolated. A complex pattern of developmental expression of the gene has been uncovered. During the proposed funding period, the investigators plan to characterize the role of HP1 in (1) organizing heterochromatin structure and (2) modifying gene expression. Two different, but complementary, approaches will be used to identify protein and DNA components that interact, directly or indirectly, with HP1. Firstly, he will immunoaffinity purify chromatin fragments to identify protein and DNA components that interact with HP1. Secondly, using the standard recombinant DNA technique of chromosome walking, he will clone and sequence the DNA found in HP1-containing heterochromatin (as defined by antibody staining) from three different extra-centromeric regions. This will identify a consensus DNA sequence that interacts with HP1 either directly or indirectly. He will then use this sequence information to design experimentally manipulatable `artificial heterochromatin' which will be placed adjacent to reporter genes in P element vectors. These P element vectors will then be used in germ-line transformation to study the role of HP1 in regulating gene expression. The investigator also would like to understand the biological significance of the developmentally expressed multiple transcripts of HP1 by (1) characterizing the HP1 transcription unit, (2) generating null mutants in the HP1 gene, (3) identifying HP1-like proteins if any, coded by the multiple transcripts, and (4) characterizing the in situ location of HP1-like proteins in the developing embryo. The results of these experiments will lead us to a better understanding of the physiology and biochemistry of heterochromatin.